Control for hot gas defrost system



Nov. 7, 1967 .1 F. CABLE I 3,350,893

CONTROL FOR HOT GAS DEFROST SYSTEM Filed Jan. 17, 1966 IN VEN TOR. Jo/m Cab/e BY United States Patent 3,350,893 CONTROL FOR HOT GAS DEFROST SYSTEM John F. Cable, Galesburg, 11]., assignor to Admiral Corporation, Chicago, 11]., a corporation of Delaware Filed Jan. 17, 1966, Ser. No. 520397 4 Claims. (Cl. 62-126) ABSTRACT OF THE DISCLOSURE A defrost control system for a home freezer having a manual defrost switch located in the door which auto matically terminates the defrost cycle upon closing the freezer door. The control system also includes an indieating light for visually indicating that the freezer is defrosting and a buzzer alarm for audibly notifying the operator that the defrost cycle is completed.

Disclosure This invention relates in general to domestic freezers, and in particular to control means for simplifying defrosting of domestic freezers which utilize the circulation of hot gases through the evaporators thereof. More particularly, this invention is concerned with a control circuit for a domestic freezer which manually or automatically terminates a defrost cycle, and means for indicating the operation and automatic termination of said cycle.

One of the more unpleasant chores associated with owning and using many commercially available home freezers is that of periodically removing the inevitable accumulation of frost and ice from the inner cabinet walls. As is well known, this accumulation is caused from the condensation of moisture entering the freezing compartment each time the freezer door is opened. Typical methods of removing the accumulation of frost and ice have been to manually dislodge it from the freezer walls by scraping; removing the contents and disconnecting the freezer, thereby allowing the accumulation to melt; or more recently, by introducing hot gases from the compressor directly into the evaporator thereby heating up the freezer walls, partially melting the ice, and easing the chore.

While the method of defrosting a freezer by circulating hot gases through the evaporator is not new, this invention improves hot gas defrosting by providing novel means for initiating the operation thereof, and a thermostat and alarm arrangement for properly terminating the defrost cycle and notifying the housewife of its termination. This invention also provides means for preventing accidental defrosting while the freezer door is closed, and enables the housewife to terminate the defrosting cycle at any time, by merely closing the freezer door. The primary object of this invention is to provide a simple and economical means for semi-automatically controlling the operation of a hot gas defrost system in a refrigeration apparatus.

Another object of this invention is to provide control means for manually initiating operation of a hot gas defrost system and for indicating the completion of a defrost cycle.

In addition, it is an object of this invention to provide means for preventing accidental defrost of a freezer while the access door is closed.

A further object of this invention is to provide means for automatically terminating a defrost cycle by closing the freezer access door.

A feature of this invention resides in a manually actuated switch mounted on the access door of a freezer in a manner which automatically de-actuates the switch and renders the defrost cycle inoperative when said door is closed.

An additional feature of this invention resides in a two position thermostat which controls the duration of the hot gas defrost cycle, and energizes an alarm to indicate the termination thereof.

Other objects and advantages of this invention will become apparent upon an examination of the following description taken in conjunction with the accompanying drawings wherein:

FIG. 1 illustrates a partially cut away perspective view of a chest freezer in which the present invention is included, having its access door in the: open position.

FIG. 2 is a diagrammatic illustration of the refrigeration apparatus and hot gas defrost system including the control means of the invention.

FIG. 3 is an enlarged view of the defrost switch showing the switch knob in two positions and also showing the depression which the knob cooperates with.

Turning to consideration of the drawings and in particular to FIG. 1, there is shown a chest type freezer which includes a cabinet 10 comprising inner walls 12, outer walls 13 insulated from the inner walls by suitable insulation 13b, and an access door or lid 14 hinged at 16. A machinery compartment 18 is provided at the bottom of the freezer and includes a hermetically sealed gas compressor 20 which normally delivers compressed refrigerant vapor through a tube 21 to a condenser 22 adjacent the outer walls wherein it is condensed to a liquid refrigerant. The liquid refrigerant is delivered through a capillary tube flow restricting device 24 (only shown in FIG. 2), in a manner well known by those skilled in the art, to an evaporator 26 surrounding the inner walls, wherein the condensed refrigerant vaporizes and absorbs heat. The refrigerant vapor is then withdrawn from the evaporator through conduit 27 having a short portion 29 (see FIG. 2) in heat transferring relation with the capillary tube, and returned to the compressor after which the refrigeration cycle is repeated.

A by-pass valve 28, controlled by an electric solenoid 32 integral therewith, is interposed in tube 21 between the compressor and the condenser. This valve allows refrigerant to flow from the compressor to the condenser during normal cooling of the refrigeration apparatus, or

" into a bypass line 30 connected thereto during the do frosting phase. The remaining end of the by-pass line extends to a point between the outlet of capillary tube 24 and the inlet of the evaporator (FIG. 2).

The solenoid which controls the bypass valve is manually energized by the operator in a manner to be explained hereinafter, and upon energization, allows hot refrigerant gas to circulate directly from the compressor to the evaporator without first going through the condenser and capillary tube. The purpose of circulating hot refrigerant gas through the evaporator is to increase the temperature of the inner freezer walls to above the freezing point of water, thereby partially melting and loosening any accumulation of ice and frost. The operator may then further remove the accumulation manually, with a substantial reduction in required effort.

Referring now to FIGS. 2 and 3, a defrost switch 40 for controlling the defrost cycle is mounted on the underside of lid 14 adjacent one edge thereof. The defrost switch includes electrical contacts 43 which are manually closed by pulling a plunger type knob 42, from its normal position, (shown in full in FIG. 3), to an extended position (dotted lines in FIG. 3). A depression 45 is provided in a top surface of wall 13, and is located directly beneath switch 40 when the lid is in its closed position. When the lid is closed and knob 42 is in its normal position, (contacts 43 open), the depth of depression 45 is sufiicient to prevent interference therewith. On the other hand, when the knob is extended and the switch contacts are closed, the bottom of the depression interferes with the knob as the lid is shut, thereby opening said switch contacts.

The arrangement of the knob mounted in the lid but in interference with the wall when the switch is closed, is an important safety feature preventing continuation of the defrost cycle upon accidental closure of the lid. This arrangement also provides an easy and convenient method of intentionally discontinuing the defrost cycle by merely closing the lid.

Defrost switch 40 connects one side of an 110 volt electrical source to solenoid 32 which, as explained above, controls the circulation of hot refrigerant vapor directly from the compressor to the evaporator. This switch is effective to begin the defrost cycle only if a regular freezer thermostat 47 which controls the compressor, is closed. If thermostat 47 is not closed, it is necessary to wait a short time for the defrost cycle to begin.

Defrost switch 46 also completes the circuit for a defrost indicating light 44 located on the front edge of the freezer door, and parallelly connected to solenoid 32. This indicating light is visible while the door is in its lowered or raised position and indicates that the defrost cycle has ether started, or is about to start, responsive to the regular freezer thermostat completing the circuit to start compressor 29.

A defrost control thermostat 50 is alfixed to inner freezer wall 12 adjacent the evaporator and consists of an expansion type bellows 52 movable responsive to the wall temperature. The bellows controls the position of a movable contact 54 which is part of a single-pole-doublethrow electric switch which closes with one contact 56 upon a decrease in temperature, and closes with another contact 58 upon an increase in temperature.

The bellows is designed and adjusted to contract at a temperature substantially below freezing, for example F. thereby closing thermostat contacts 54-56, and enabling defrost switch 40 to control solenoid 32. At a temperature slightly above freezing, for example 35 F, the bellows expand and previously closed switch contacts 5456 open, thereby disconnecting solenoid 32 and closing 'by-pass valve 28 which discontinues the by-pass flow of refrigerant and returns the refrigeration apparatus to normal cooling operation. Simultaneously, thermostat contacts 54-58 close, completing the circuit to an alanm buzzer 60 located in the machinery compartment. The buzzer emits an audible sound notifying the operator that the inner freezer walls have reached a temperature sufficient to partially melt the accumulated ice and frost. This accumulation may now be easily removed, or depending upon the conditions, may dislodge from the walls by its own accord.

Frost and ice which have melted and collected at the bottom of the freezer may be discarded through a drain 62 provided on the freezer bottom and communicating through a wall of the freezer cabinet.

After the defrost cycle has been completed, contacts 43 of defrost switch 40 are opened thereby disconnecting the alarm buzzer and indicator light, and rendering the defrost cycle inoperative. These contacts are opened by urging knob 42 inwardly to its normal position, either by pushing it manually or merely closing the lid whereby the knob will contact the bottom of depression 45. During this time, the compressor is running since the freezer temperature is above that required to close freezer thermostat 47. Opening defrost switch 40 prevents initiation of the defrost cycle when the freezer wall drops to 10 F., and switch contacts 5456 return to their closed position.

Operating defrost switch 40' by merely closing the access door is an important advantage should it be necessary or desired to rapidly terminate the defrost cycle such as when called away from the freezer. In such a case, the single step of closing the freezer door will suffice for what normally would be a two-step operation of first turning off a switch and then closing a door.

What has been described is an automatic means for terminating at defrost cycle in a domestic freezer, and for indicating operation and termination thereof by visual and audible means, respectively. In addition, a safety device has ben provided which renders the defrost cycle inoperative while the access door is in a closed position and automatically terminates the defrost cycle upon closing said door.

It is obvious that upon study by those skilled in the art the disclosed invention may be altered or modified both in physical appearance and construction without departing from its inventive concept. Therefore, the scope of protection to be given this invention should not be limited by the embodiment described above, but should be determined by the essential descriptions thereof which appear in the appended claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

What is claimed is:

1. In combination with a refrigerator cabinet having walls defining a food storage compartment provided with an access opening therein, a movable door for opening and closing said access opening, a cooling element in thermal contact with said walls, refrigerating apparatus for normally maintaining said walls at a temperature substantially below the freezing point of water; defrost valve means integral with said refrigerating apparatus for modifying said apparatus to heat said walls; control means actuating said defrost valve means for selectively initiating or terminating modification of said refrigerating apparatus; said control means mounted in said door in a position for manual operation when said door is open, and in a position of interference with one of said cabinet walls upon closing said door, said position of interference terminating modification of said refrigerating apparatus, means indicating the operational mode of said refrigerating apparatus, and temperature responsive means automatically deactuating said defrost valve means for terminating modification of said refrigerating apparatus upon the temperature of said walls rising above the freezing point of water.

2. The combination as set forth in claim 1 wherein said indicating means includes audible alarm means operable responsive to operation of said temperature responsive means for audibly indicating termination of the modification of said refrigerating apparatus.

3. The combination as set forth in claim 1 wherein said indicating means includes an indicating lamp operable with actuation of said defrost valve means for providing a visual indication that the refrigerating apparatus is in its defrost mode.

4. The combination as set forth in claim 1 wherein said indicating means includes an indicating lamp energizable with actuation of said defrost valve means, and audible alarm means operable responsive to operation of said temperature responsive means.

References Cited UNITED STATES PATENTS 2,957,316 10/1960 Buchanan 62153 3,005,319 10/1961 Buchanan 62l53 X 3,028,586 4/1962 Reda 62l26 FOREIGN PATENTS 613,819 l/1961 Canada.

MEYER PERLIN, Primary Examiner. 

1. IN COMBINATION WITH A REFRIGERATOR CABINET HAVING WALLS DEFINING A FOOD STORAGE COMPARTMENT PROVIDED WITH AN ACESS OPENING THEREIN, A MOVABLE DOOR FOR OPENING AND CLOSING SAID ACCESS OPENING, A COOLING ELEMENT IN THERMAL CONTACT WITH SAID WALLS, REFRIGERATING APPARATUS FOR NORMALLY MAINTAINING SAID WALLS AT A TEMPERATURE SUBSTANTIALLY BELOW THE FREEZING POINT OF WATER; DEFROST VALVE MEANS INTEGRAL WITH SAID REFRIGERATING APPARATUS FOR MODIFYING SAID APPARATUS TO HEAT SAID WALLS; CONTROL MEANS ACTUATING SAID DEFROST VALVE MEANS FOR SELECTIVELY INITIATING OR TERMINATING MODIFICATION OF SAID REFRIGERATING APPARATUS; SAID CONTROL MEANS MOUNTED IN SAID DOOR IN A POSITION FOR MANUAL OPERATION WHEN SAID DOOR IS OPEN, AND IN A POSITION OF INTERFERENCE WITH ONE OF SAID CABINET WALLS UPON CLOSING SAID DOOR, SAID POSITION OF INTERFERENCE TERMINATING MODIFICATION OF SAID REFRIGERATING APPARATUS; MEANS INDICATING THE OPERATIONAL MODE OF SAID REFRIGERATING APPARATUS, AND TEMPERATURE RESPONSIVE MEANS AUTO- 